This invention relates to batteries.
Batteries, such as primary alkaline batteries, are commonly used as energy sources. Generally, alkaline batteries include a cathode, an anode, a separator, and an electrolytic solution. The cathode can include an active material, such as manganese dioxide or nickel oxide, carbon particles that enhance the conductivity of the cathode, and a binder. The anode may be, for example, a gel including zinc particles as the active material. The separator is disposed between the cathode and the anode. The electrolytic solution can be, for example, a hydroxide solution that is dispersed throughout the battery.
Desirable primary alkaline batteries have a high energy density and low capacity loss upon storage. Capacity retention upon storage can be important in primary battery systems where, unlike secondary battery systems, capacity cannot be recovered through recharging. Primary batteries having nickel oxide cathodes and amalgamated zinc anodes have high energy densities, but can lose significant amounts of capacity upon storage at 60xc2x0 C. Self-discharge, either by hydrogen reduction or oxygen evolution from the nickel oxide cathode can result in loss of discharge capacity and formation of non-conductive regions.
The invention features a primary alkaline battery including a nickel oxyhydroxide cathode. The battery preferably has a capacity loss after storage for 2 weeks at 60xc2x0 C. of less than 40 percent. The cathode can include a cobalt oxyhydroxide-modified nickel oxyhydroxide or non-fractured nickel oxyhydroxide, which can improve the capacity loss proper ties of the battery.
Cobalt oxyhydroxide-modified nickel oxyhydroxide is a nickel oxyhydroxide having cobalt oxyhydroxide on a portion of the surface of the nickel oxyhydroxide. For example, the cobalt oxyhydroxide-modified nickel oxyhydroxide can be nickel oxyhydroxide having a coating of cobalt oxyhydroxide on a nickel oxyhydroxide. The coating can be substantially uniform, meaning that the coating covers at least 60% of the surface of the nickel material.
The nickel oxyhydroxide can be substantially non-fractured. Non-fractured nickel oxyhydroxide is nickel oxyhydroxide that is formed from nickel hydroxide by oxidation and inter-layer spacing contraction or no change in inter-layer spacing. For example, when xcex1-Ni(OH)2 is used as the precursor the degree of fracturing can be significantly reduced because xcex1-Ni(OH)2 has an inter-layer spacing of about 8 xc3x85, which contracts upon formation of xcex3-NiOOH to about 7 xc3x85. Alpha nickel hydroxide, xcex1-Ni(OH)2, is a class of nickel hydroxide materials that has the general formula:
(Ni1xe2x88x92nAn)(OH)2Xn/mxc2x7(H2O)z
where A is Al, Co, Fe, Mn, or other trivalent metal ion, or a mixture thereof,
X is an anion having charge of -m, m being 1 or 2,
n is between zero and 0.8, inclusive, and
z is between 0 and 0.3, inclusive. X can be a halide, carbonate, carboxylate, sulfate, sulfite, phosphate, or phosphite. Preferably, A is Al, Co, Fe, or Mn, or a mixture thereof, X is CO32xe2x88x92(m=2), NO3xe2x88x92(m=1), Clxe2x88x92(m=1), or SO42xe2x88x92(m=2) and n is between zero and 0.3.
In one aspect, the invention features a primary alkaline battery including a cathode, an anode, a separator, and an alkaline electrolyte. The cathode can include a cobalt oxyhydroxide-modified nickel oxyhydroxide or a nickel oxyhydroxide derived from xcex1-Ni(OH)2. The nickel oxyhydroxide can be xcex3-NiOOH. The nickel oxyhydroxide can be substantially non-fractured.
In another aspect, the invention features a method of manufacturing an alkaline battery. The method includes assembling a cathode, an anode, a separator, and an alkaline electrolyte to form the alkaline battery. The method can include forming a cathode including the nickel oxyhydroxide. The method can also include forming a cobalt oxyhydroxide-modified nickel oxyhydroxide or non-fractured nickel oxyhydroxide. Forming the nickel oxyhydroxide can include converting xcex1-Ni(OH)2 to nickel oxyhydroxide, for example, by exposing nickel hydroxide to ozone.
In yet another aspect, the invention features a method of decreasing capacity loss in a nickel oxyhydroxide primary alkaline battery. The method includes forming a cathode including a nickel oxyhydroxide, and assembling the cathode, an anode, a separator, and an alkaline electrolyte to form the alkaline battery. The method can include converting xcex1-Ni(OH)2 to the nickel oxyhydroxide or converting cobalt hydroxide-coated xcex1-Ni(OH)2 to the nickel oxyhydroxide.
In another aspect, the invention features a cathode for a primary battery including non-fractured nickel oxyhydroxide or a cobalt oxyhydroxide-modified nickel oxyhydroxide.
The anode can include zinc.
In preferred embodiments, the cathode further includes an oxidizing additive. Reduction reactions at the surface or in the bulk of the nickel oxyhydroxide particles, which can lead to decreased storage capacities, can be partially eliminated or prevented by including oxidizing additives in the cathode. Electrochemically active additives are preferred to reduce oxygen evolution by raising the overpotential to avoid losses in capacity that can result from the use of electrochemically inactive additives.
Other features and advantages of the invention will be apparent from the description and drawings, and from the claims.